br>So I just finished building my MidiDAC convertor today. It is my third module after a 2u COTA and an Oakley VCO.

The first abnormality i noticed was that all three modules did not seem to work at once, only 2 plugged in would work. I then found only 1 socket for the Midi interface which worked when the other two were plugged in, which i thought was quite odd. I disassembled the back panel and checked the soldering on the dizzy board. After checking, and reassembling everything seemed to work properly.

I noticed a strange smell when calibrating the midi interface and finally noticed that it was coming from the PSU. The back panel was too hot to touch and the heat seemed to be coming from the Q1 TIP145 transistor. I immediately turned off the unit and also noticed that the -ve LED does not power.

What can I do to solve this? Did the Mididac cause a current overload? Thats one of the only explanations i can think of, but it doesn't make sense considering I was only running 3 modules. br> br>

br>welhamc

br>I just remembered that I trimmed the legs of both power transistors as I clearly forgot to at the time. Could this have damaged them? br> br>

br>welhamc

br>For some reason the -ve led doesn't light when the MidiDAC is plugged into the top left dizzy connector.

Now that I've rearranged the connections on the dizzy the green led has come back on. What is the possible problem here? br> br>

br>Synthbuilder

br>If either the +15V or -15V LED goes out on the PSU board then you have a short on that particular power line. That is -15V is being dragged to 0V by an unwanted connection.

If at one point the midiDAC could be calibrated one possible cause is an intermittent short to 0V on the midiDAC board itself. One cause of a board working then not is an electrolytic capacitor fitted the wrong way around, but it could also be a small bit of metal wedged somewhere on the board - a small wire clipping under an IC is possible.

All the headers on the Dizzy are identically connected but an intermittent short between the wires on the plug of the cable can cause confusing results like this too. A change in the angle of the wires as they enter the plug can make or break an unwanted contact.

So I'd check the cables again - visually first. Then plug them into a powered up Dizzy but not any modules, wiggle them and see what happens to the LEDs. Any lights go out and you have a problem with the cables.

It will be worth checking that the PSU is still producing +15V and -15V too.